An ongoing trend within telecommunications is the convergence of fixed and mobile networks, which is known as Fixed Mobile Convergence (FMC). The trend of evolving networks using IP-based technologies is common for fixed and mobile networks, which makes the convergence easier. By FMC, mobile and fixed network operators will be able to utilize their network resource more efficiently, which leads to reduction of capital and operational expenditure (CAPEX and OPEX). For instance, when a user is running an IP-based application such as Multimedia Telephony (MMTeI) inside their home, it is more efficient to utilize broadband connectivity of the fixed access network rather than the wireless access network.
Residential networks are a key to the success of FMC because they are the most commonly used fixed network access by ordinary users. Therefore, it is important to be able to connect mobile phones to the Evolved Packet Core (EPC; see “Architecture enhancements for non-3GPP Accesses,” 3GPP TS 23.402, V8.2.0, 2008-06) through a residential network. The term User Equipment (UE) can be used in place of the term mobile terminal or mobile phone; the term UE is familiar in the 3rd Generation Partnership Project (3GPP) documentation.
3GPP defines mobile 2G/3G/LTE accesses and “non-3GPP accesses” (TS 23.402). The latter can be a fixed network. The BBF (BroadBand Forum, the standardization organization for the fixed access; see http://www.broadband-forum.org/) defines an architecture for fixed networks. Many UEs address the FMC trend by providing multiple radio interfaces: one interface to connect to a 2G/3G/LTE access and a WiFi interface to connect to a fixed network.
There is an ongoing joint work item on FMC between these two organizations [3GPP TR 23.839 and BBF WT 203]. A 3GPP UE can attach to a BBF access network and connect to one or more Packet Data Networks (PDNs) via the S2 interface [3GPP TS 23.402]. FIG. 1 of the accompanying drawings is a schematic block diagram providing an architecture overview, illustrating a UE 2 connecting to a 3GPP domain 4 via a BBF domain 6. The BBF domain 4 comprises a Residential Gateway (RG) 8, an Access Node 10 and a Border Network Gateway (BNG) 12. The 3GPP domain 4 comprises one or more PDN Gateways (PGWs) 14.
The S2 interface comes in three types: S2a, S2b and S2c. The latter two overlay the BBF network and do not impact the BBF. S2a is a more converged solution that does impact BBF nodes.
In S2a, there is a GPRS Tunnelling Protocol (GTP) or Proxy Mobile IP (PMIP) tunnel for each PDN connection between the BBF BNG and the 3GPP PGW(s). Each PDN connection is anchored in a 3GPP PGW. The UE receives one IP address for each PDN connection, and it is the PGW that assigns the address. Between the UE 2 and the BNG 12 a point-to-point link is provided in order to separate the traffic from the different PDN connections.
Such a point-to-point link can be implemented in several ways. An assumption can be made that the network between the UE 2 and the BNG 12 is Ethernet-based. All nodes intermediate the UE 2 and the BNG 12 do forced-forwarding towards the BNG 12 on L2 (Ethernet). The BNG 12 sends downstream traffic targeted for the UE 2 as unicast on L2, even if that traffic is multicast/broadcast on L3 (IP).
Such an implementation imposes a limited impact on the UE 2 and the existing BBF infrastructure. More importantly, there is no impact to the UE 2 if the UE 2 only has one default PDN connection. The BNG 12 can distinguish the different PDN connections based on UE MAC address combined with the PDN connection IP address that was assigned to the UE 2.
There are other ways to implement a point-to-point link between the UE 2 and BNG 12. Examples are: a L3 tunnel (e.g. IPsec or IP-in-IP), a L2 tunnel (e.g. L2TP), and so on. However, all of these tend to have a greater impact on the UE 2 or the BBF infrastructure.
The present applicant has appreciated a problem with the above-described architecture. In particular, it has been appreciated that there could be a situation where a set of one or more PGWs assign the same IP address for different PDN connections. This could occur where, for example, there are two PDNs connections relating respectively to two closed corporate networks, each with their own addressing scheme. Each PDN might be served by a different PGW, and each PGW might be managed by a different operator. The 3GPP domain(s) and the UE are designed to handle such an overlap without any issue. However, the problem is that the BNG will get confused; it will no longer be able to map upstream traffic to the correct GTP/PMIP tunnel.
It should perhaps be noted that the likelihood of such a problem occurring in a real deployment is small; most UEs will only use a single PDN connection, and the IP addressing schemes of different PDNs will in most cases not overlap. However, the problem can and will occur without a solution, and the present applicant has appreciated the desirability of addressing this issue.